Our work involves the characterization of a number of calcium regulated systems functioning to control the contraction of vertebrate smooth muscle. In particular we have been studying the multifunctional calcium binding protein calmodulin, focusing on its role as a regulator of cyclic nucleotide levels, through its influence on phosphodiesterase activity, and its role as a modulator of the activity of the myosin light chain kinase. Having purified calmodulin dependent phosphodiesterase from vertebrate smooth muscle we intend to characterize the enzyme, including its interaction with calmodulin, and to compare its properties to those of two other phosphodiesterases present in this tissue. We have purified myosin light chain kinase to homogeneity and are presently attempting to raise antibodies to this protein to use in quantitation, localization and characterization studies and also to use in studies of the role of the enzyme in smooth muscle regulation. We have raised antibodies to calmodulin which we intend to use in the localization of calmodulin in smooth muscle and to probe the proteins interactions with the various enzyme systems. We are also currently establishing a radioimmunoassay procedure which will help quantitate calmodulin in various tissue fractions.